Process for continuous purification of bulk fiber



SERCH @ONE Feb. 7, 1961 v. M. KUMIN ETAL PROCESS FOR CONTINUOUS PURIFICATION OF' BULK FIBER Original Filed Aug. 9, 1956 4 Sheets-Sheet 1 Feb. 7, 1961 v. M. KUMIN Erm. 2,970,882

PROCESS FOR CONTINUOUS PURIFICATION OF BULK FIBER Original Filed Aug. 9, 1956 4 Sheets-Sheet I5 Trag/vers Feb. 7, 1961 v. M. KUMlN ErAL PROCESS FOR CONTINUOUS PURIFICATION 0F BULK FIBER Original Filed Aug. 9, 1956 4 Sheets-Sheet 4 INVENTORS V/cToe M. ,VUM/1v, HND TeA-ov H. H041. l s rae rrae/VEXS- United States Patent O "i PROCESS FOR CONTINUOUS PURIFICATION F BULK FIBER Victor M. Kumin, Newton Highlands, Mass., and John H. Hollister, Lake Bluff, lll., assignors to The Kendall Ctztmpany, Boston, Mass., a corporation of Massachuse s Continuation of application Ser. No. 603,127, Aug. 9, 1956. This application Dec. 3, 1958, Ser. No. 778,034

9 Claims. (Cl. 8-108) This invention relates to the continuous treatment of fiber material. More particularly the invention relates to the removal of shell and other impurities from bulk ber, particularly bulk cotton fiber, by continuous ow methods, and to apparatus for effectively accomplishing these purposes.

When received from the field, bulk cotton contains appreciable amounts of various contaminants such as seeds, leaves, pods, stalks and dirt of various kinds, which we hereinafter refer to collectively as shell. Although conventional mechanical processes, such as ginning, opening, carding, combing, and the like, are capable of removing a large portion of these undesirable impurities, a substantial amount of the shell remains associated with the fiber and cannot be removed therefrom even with repeated mechanical processing. This is due at least in part to the fact that some of the larger particles of shell are triturated by the mechanical treatment with the formation of finer particles which are immediately dispersed into the mass of fiber and become exceedingly difficult to remove.

In addition to shell, bulk cotton fiber also contains substantial amounts of other forms of contaminating substances or impurities, such as waxes, oils, fats, pectins, proteinaceous materials and like substances, both organic and inorganic, which are hereinafter referred to as fats, waxes and inorganic impurities. These fats, waxes and inorganic impurities impart 'a greyish color to the fiber and make the cotton substantially non-absorbent. Accordingly, for many applications and uses of cotton it is essential that the various impurities mentioned hereinabove be separated therefrom. Although in some instances this can be suitably accomplished after the fiber has been spun into yarns, in other instances, as for example in the manufacture of absorbent, surgical or jewelers cotton, it is necessary to remove the impurities from the fiber while it is in bulk form.

The removal of impurities from cotton fibers has been accomplished in the past by a variety of methods which are commonly designated broadly in the art as boiling and/or bleaching processes. Until recently, however, virtually all of these conventional boiling and/ or bleaching processes were of the batch type, and for this reason were cumbersome and slow and subject to numerous objectons from a cost standpoint.

While there are many variations, in general these processes follow a pattern wherein the cotton, in the form of either fiber, yarn or fabric, is introduced into a reaction vessel of the type known as a kier along with a suitable alkaline solution, such as a hot aqueous solution of caustic soda and soap. This hot alkaline solution is customarily circulated through the kier for a period of eight to twelve hours at temperatures of about 250 F. and at a gauge pressure of approximately fifteen pounds per square inch. The goods are then washed in fresh water, usually in the kier itself. However, if preferred, they may be removed to a separate vessel for this purpose or for subsequent bleaching operations. After the wash- 2,970,882 Patented Feb. 7, 1961 ing, the material is treated with a chlorine-containing or peroxide-containing bleach solution, such as a solution of sodium or calcium hypochlorite o1' an alkaline solution of sodium or hydrogen peroxide, while maintaining the solution at temperatures of approximately to 100 F. for chlorine bleaches and to 200 F. for peroxide bleaches. The fiber, yarn or fabric is then treated with a dilute sulphurc or hydrochloric acid solution to neutralize the excess alkaline material and dissolve acidsoluble substances. The fiber, yarn or fabric is finally washed again and neutralized, whereupon it may be treated with a finishing agent.

For reasons of economy, batches of material undergoing boiling and/or bleaching treatment should be of substantial size. Each kier, for example, is generally loaded with a quantity of cotton of the order of 3,000 or more pounds (dry basis). Batches of this size, however, cause the process to be exceedingly slow and require as much as 48 to 72 hours for the complete operation. Moreover, large amounts of pumping, loading and unloading equipment, and many operators are required for loading and unloading the kiers and maintaining the correct amount of the appropriate ingredients in the proper treating vessels.

In recent years the literature has disclosed a number of processes wherein substantially continuous lengths of cloth have been boiled and bleached in what are tantamount to continuous process conditions. These processes are highly eliicient for cloth in that they do not require as many operators nor the throughput time normally encountered in batch operation. However, while substantially all of these processes are highly suitable for the bleaching of fabrics, to the best of our knowledge none of them is suitable for handling bulk fiber, nor can they readily be adapted to the handling of bulk cotton.

The elimination of contaminating substances from bulk cotton presents a number of problems which are not encountered in the purification of cotton yarn or fabric. In the first place, cotton that is fabricated into yarns or cloth is subjected to many mechanical operations which are not required in the preparation of bulk fiber. In each of these additional operations, one or more increments of contaminating materials is removed. Accordingly, when fibrous raw material in bulk form is introduced into the purification process, it normally contains substantially more impurities than are present in yarns or fabrics.

Secondly, while yarns or fabrics are normally of substantially uniform bulk density and thickness, fiber in bulk form is highly variable in these respects. This renders it considerably more dificult to obtain uniform penetration of bulk masses by purifying reagents than it is to obtain uniform penetration of yarns or fabrics. Furthermore, the dimensions of a bulk fibrous mass change rapidly when the mass is subjected to slight stress, making manipulation in process extremely troublesome, whereas yarn or fabric is capable of withstanding considerable stress without appreciable deformation. This capability facilitates the handling of yarn or fabric. Thus the vary nature of cotton in bulk fiber form makes it substant'ally more difficult to purify than cotton yarns or fabric.

Heretofore, a prolonged batch process involving an 8-10 hour pressure boil with caustic soda was deemed to be essential in the purification of bulk cotton. Th's long pressure boil was required by the presence of the large amounts of impurities normally associated with bulk fibrous raw material, the dimculties of attaining uniform penetration of solutions throughout the non-uniform mass, and the difficulties in obtaining uniform temperature distribution throughout the mass of bulk fiber. Accordingly, until our discovery, the continuous bleaching of bulk cotton has been considered a virtual impossibility because of the prolonged caustic pressure boil, heretofore thought necessary, and the nature of the fibrous mass as set forth hereinbefore.

It is, therefore, a primary object of this invention to provide a continuous process for producing purified cotton textile fiber in bulk form.

Since the process of our invention is adaptable to the purification of other bulk natural cellulosc fibers such as linen, ramie, and many of the other bast fibers, as well as cotton, it is a further object of this inven ion to provide a continuous process for purifying such bulk textile length fibrous and/ or fiberlike materials in general.

A further object of this invention is to el'minate the pressure boil step in the purification of bulk cotton fiber.

A further object is to provide a continuous process for preparing bulk cotton for treatment with bleach.

Another object is to provide a continuous process for removing shell from bulk fiber.

A further object is to provide a continuous process for bleaching bulk fiber.

A further object of this invention is to provide a continuous process for use in the manufacture of absorbent cotton.

A further object of this invention is to provide a continuous process for purifying bulk cotton under controlled and predictably uniform process conditions.

A further object of this invention is to provide such a process which affords great economies in process time, space, water and chemicals.

Still further objects and advantages of the invention will appear from the following description and appended claims.

Before explaining in detail the present invention, however, it is to be understood that the invention is not limited in its application to the details described herein, since the invention is capable of other embodiments and of being practiced or carried out in various ways.

The invention is based on the surprising discovery that bulk fibrous material may be stripped of its impurities by introducing the fibrous material in the form of a loose, uncompacted mass into a conveyor system and at a plurality of points along the system subjecting the fiber to direct contact with liquid solutions of various cleaning and bleaching reagents, causing the wetted fiber mass to pass between squeeze rolls to effect adequate distribution of solutions in the fiber mass, controlling the forward progress of the conveyor so that the time periods required to move the fiber between points of the conveyor system where the various solutions are introduced are so regulated that the fiber impurities and solution are allowed to remain in commingled relationship for a sufficient period to enable reaction between the solution and contaminants and fiber to proceed to the desired extent, and removing the cleaned fiber from the system in sufiicient volume to prevent uncontrollable continuous and undesirable build-up of fiber in the system.

Also, and much to our surprise, we have found' that by the practice of our invention we can eliminate the expensive and time-consuming step of pressure boiling the bulk fibrous materials for an extended period of eight hours or more.

Going into more detail, we have found that, if the purifying solutions with which the bulk fiber is treated are rapidly and properly distributed and diffused in and throughout the mass of fiber, the process of purifying the cotton can be greatly hastened and the purification of the cotton can be carried out in a continuous fashion.

We have found that the necessary diffusion and distribution of the cleaning liquid in the mass of fiber can be accomplished by subjecting the fiber mass to direct contact with the purifying liquid and then causing the wetted fiber to pass through an equilibrating nip. The function of the equilibrating nip is to distribute and disperse the liquid in and among the fibers, and to predetermine the amount of said liquid to be retained by the bulk liber. While this function can also be accomplished by passing the wet ber mass over a vacuum box, we prefer to use a roll nip because we find it to be far more efficient in distributing the liquid in the fiber mass. This nipping step greatly hastens the time of reaction between the liquid and the bulk fiber and its impurities. By allowing an appropriate amount of time for reaction between the fiber impurities and chemical substances which are dispersed in the bulk liber, we can accomplish the desired reaction between the chemical, the fiber and the fiber impurities in a fraction of the time required by the batch process. And by combining a series of solution treatments of the same general type we have developed a continuous process of purifying bulk cotton.

These and other salient characteristics and objects of our invention will be understood and appreciated better from the following description of a preferred embodiment which is selected for the purpose of illustration and is shown in the accompanying drawing in which:

Figures 1 and l-A are flow sheets representing the process schematically and step by step;

Figure 2 is an enlarged fragmentary view showing diagrammatically one suitable form of aging device which may be used to provide the necessary reaction time between solution and fiber mass in carrying out our process;

Figure 3 is a cross-sectional view along line 3-3 of the aging device shown in Figure 2; and

Figure 4 is an enlarged diagrammatic side elevation of another form of aging device Which may be used to provide the necessary reaction time between solution and fiber mass in carrying out our process; it is shown in Figure 1 outlined by the broken line 4, and it may be used alone or in conjunction with the apparatus of Figure 2.

Referring first to the flow sheet of Figure 1, bulk cotton received in bales is introduced into conventional bale opening equipment 10, from which it is delivered, va suitable conventional means, to a mechanical weighing and feeding mechanism 12, of which there are several suitable and well-known types, such as a fiber lapper or gravimetrio fiber feeder. In such feeding mechanism, the unpurified cotton is formed into a loose mass of substantially controlled unit weight per cubic foot whence it passes into the conveyor system beginning with conveyor belt 14.

The linear rate of feed and thickness of the loose mass will depend on the pounds per hour throughput desired; on the capacity of the other components of the system to be described more fully hereinafter; on the time required to wet out the cotton, which is related to the amount and nature of impurities therein; and on the observed degree of fiber contamination due to shell, etc., which in turn depends on the source of liber and initial mechanical cleaning thereof. We prefer to use a loose mass in the form of a web of from l-4 inches in thickness having an initial dry weight as it reaches the conveyor of between .l5 and .9 pound per square foot, or between .45 and 10.8 pounds per cubic foot, although the thickness of mass is not critical.

The conveyor belt 14 is preferably of an open-mesh construction, so that the liquid solutions, all of which are applied in excess, may drain through it. The conveyor belt must be able to withstand the chemical action of the solutions which are applied and, therefore, the selection of materials for the construction of the belt should be made with this fact in mind. We have found that stainless steel of the 316 type is satisfactory for this purpose, although a number of metals, plastics or rubberlike materials could also be employed.

While on the conveyor belt 14, the bulk cotton is brought into direct contact and saturated with a 1 to 8%, and preferably 3 to 4%, solution of hot caustic soda. This may be accomplished by directing sprays of caustic solution at the web as it moves along belt 14. As inagresse dicated in the drawings, the desired solution is made up iu tank 16 and is conveyed via line 18 and nozzles 20 and 20A to the web. A pump 22 is provided in line 18 to furnish the desired pressure in the caustic system. Following the saturation, the web of cotton is conveyed to the nips 24 and 24A of rolls 26 and 26A. As the cotton passes through the nips, the caustic is dispersed in and among the fibers and into the contaminants of the bulk fiber, and the excess solution is expressed from the mass. The speed of the belt will vary depending on the thickness and weight of the web, but ordinarily will move at a speed of from 6 to 12 feet per minute, more or less. Pans 28 are provided immediately beneath the rolls and extend to points ahead of the rolls at which the solution is applied to the web to collect the excess solution. Lines 30, which attach to pans 28, convey the excess solution back to tank 16.

In lieu of sodium hydroxide, lithium hydroxide, potassium hydroxide, soda ash or other alkaline substances may also be used provided the concentrations of the solutions are adjusted to take into account the reactivity of these alkaline materials as compared to sodium hydroxide in water. Small amounts of wetting agents and dispersing agents including soaps and detergents may also be added to assist the initial caustic wet-out process. The solutions as applied are preferably at temperatures in excess of 150 F., and as close to the boiling point of water, that is, 212 F., as is possible.

To assure the complete wet-out of the cotton, we prefer to use a ratio of 40 unit weights of solution per unit weight of web. Also, we prefer to apply the solution and squeeze out the excess at a plurality of locations as indicated in the drawings, although it is possible to accomplish the desired wet-out of the cotton with caustic by a single unit of spray followed by a press roll.

Other methods of applying caustic solution to the cotton, which may be used in accordance with our invention, include the use of flooders, or the utilization of saturating pans followed by squeeze-out rolls, or sprays may be used in combination with ooders and/or saturating pans.

As the cotton web leaves the nip 24A of rolls 26A, it contains caustic solution in an amount by weight between 75 and 400% based on the dry weight of the cotton. The amount of solution in the web is controlled by controlling the pressure applied to the rolls 26A. Pressure-controlling means (not shown) of any conventional type are provided for the rolls 26 and 26A. Accordingly, as the web leaves the nip 24A, each pound (dry weight) of web preferably contains approximately between .02 and .08 lb. (dry weight) of caustic.

At least some of the reactions between the caustic and the impurities of the bulk liber require time to proceed suciently, so that their effect is noticeable. Accordingly, it is necessary to maintain the caustic and bulk brous material in a commingled relationship for this required time. Also, elevated temperatures promote the reaction, and therefore we prefer to conduct this step of our process at relatively high temperatures. Temperatures of about 212 F. are most suitable for this step of our process, but this temperature is not critical and we may use temperatures as low as 150 F.

In carrying ont the reaction between alkali and cellulose bers, it is desirable to exclude air, since the alkali in the presence of oxygen may damage the cellulose liber. The damage to which we have reference is referred to by those skilled in the art as degradation and is evidenced by a reduction in the chain length of the molecules of cellulose in the liber. To minimize degradation, we prefer to conduct this phase of our process in substantial absence of air.

Accordingly, we have found it desirable to provide a section of the conveyor system wherein the cotton may b e retained at elevated temperatures in substantialv absence of oxygen (air) for a period of from twenty minutes to four hours. In order to provide the required time period without unduly lengthening our conveyor system, we prefer to slow down the forward progress of the saturated liber at this section of the conveyor system. We refer to this section of our conveyor system as the aging section, and we refer to the time during which the cotton is in the aging section as the aging time.

There are, of course, many conventional ways of accomplishing the aging step such as by providing a travel of suicient length, or utilizing the principle of pleating the brous web on a belt as is shown in Figure 4, or by providing an inclined heated rotary drum, each of said devices providing the desired throughput time characteristics, as does our preferred apparatus such as diagrammatically indicated in Figure 1, and more clearly shown in Figures 2 and 3.

As therein noted, our preferred aging device includes a tower 36 consisting of three essentially vertically disposed side members 38, 40 and 42 and a side 44 which slopes outwardly from the top to the bottom. The amount of the slope or inclination from the vertical is not great, being only sufficient to prevent the tendency of the saturated cotton to bind itself within the tower, due to its natural packing characteristics. It should be appreciated that while we have shown our tower as having a substantially rectangular cross-sectional area, there is nothing critical about the geometry of the cross section of the tower, and to the best of our knowledge any convenient cross-sectional shape may be used.

The entire tower is supported on suitable brace members 48 and 50 and fastened by appropriate fastening means 54, and the braces are supported in position by standards 56 on and from which the entire age tower structure and most of its components are suspended.

The capacity of the tower will, of course, depend on the contemplated throughput. We prefer to employ a tower having suiicient capacity to hold between two and four hours throughput. For example, contemplating a 400 pound per hour throughput, the tower should be made large enough to hold from 800 to 1,600 pounds (dry weight). mended, however, since heat losses from such towers are larger and detract from the economies of our process.

At the top of the tower a pair of intermeshing toothed rolls 58 and 60 are held in position by brace members 62 and 64 through suitable bushings or bearings 68 and 70. The upper roll 58 is positioned so that its teeth 72, which may be of any convenient size, and are preferably from 1/2 to 2" in length, engage the web of saturated cotton as it leaves the belt 14. This roll is driven by a motor (not shown) in the same direction as that of belt 14, and at the same or somewhat greater speed than the speed of belt 14. Beneath roll 58, and traveling in a reverse direction to it and at higher speeds than roll 58, is roll 60, having outwardly extending teeth 76 which are positioned along the roll so that they encounter, but do not interfere with the teeth 72 of roll 58.

The cotton leaving belt 14 is picked up by teeth 72 of roll 58 and is carried around the roll to a point where it encounters the teeth 76 of roll 60, which are rotating in opposed direction to roll 58. The web is comminuted by passing through the rolls 58 and 60, and in the cornminuted state drops into tower 36. While it is not essential that the web be comminuted for further processing in accordance with our invention, we find that comminution facilitates the handling of the bulk fiber in and away from the aging tower.

The bottom surface of the aging tower 36 consists of a conveyor belt 78 which may be driven at a controlled speed by a motor (not shown). 'Ihe conveyor belt 78 is preferably disposed at a slight angle; i.e., about 20 with the horizontal, to facilitate the removal of the treated liber from the tower. The side members, 38, 42

and 44, extend from immediately beneath the conveyor` Extremely large towers are not recombelt 14 to conveyor belt 78. Side member 40 extends from immediately beneath the conveyor belt 14 to a line located about a foot or a foot and a half above the conveyor belt 78, so as to provide an opening 80 in side 40, through which the treated product may be evacuated from the aging tower. wer prefer to use a pair of toothed rolls 82 and 84, which facilitate the removal of the cotton from the aging tower in much the same way as rolls 58 and 60 assist in introducing the web to the tower. Rolls 82 and 84 may be suspended from standards 56 by conventional supporting means 83 and 85 and driven by a motor (not shown).

As previously indicated, the reaction of the caustic with the constituents of the bulk fiber mass is enhanced by elevated temperatures. Accordingly, we provide means for furnishing heat to the aging tower. While any convenient means for furnishing this heat may be used, we prefer to use a plurality of steam injectors 86 through which steam is introduced directly into the fiber mass through holes 87 provided in side members 38, 40, 42 and 44.

The steam not only furnishes the desired heat, but in large measure excludes air from the aging tower. 'Ihe steam is furnished to these injectors from a steam line 88 which connects to an appropriate generating plant not shown. Instead of using steam we can, of course, use other heating methods such as electric coils, and use an inert gas such as nitrogen as a purge gas to exclude substantially all air, or we may use an inert gas, which has been preheated to the desired temperature, as the heating medium. When an inert gas is used as heating medium instead of steam, care must be exercised to avoid excessive loss of liquids from the fiber during the heating and aging step.

When the process is first started and the saturated fiber is first admitted to Ithe aging tower, the conveyor belt 78 is not in motion. Steam is admitted into the aging tower and the bulk liber is allowed to build up therein for the period which is required for the reaction of caustic with the bulk fibrous constituents. At the end of this period, which ordinarily is between twenty minutes to four hours, the conveyor belt 78 and rolls 82 and 84 are set in motion at such a speed that the amount of cotton leaving the tower 36 per unit time is substantially equal to the amount of cotton which is being admitted to the tower.

From conveyor belt 78 the fiber is passed through a conventional wet stock feeder 89, where it is further comminuted and formed into a loose, uncompacted mass which is deposited on conveyor belt 90, which, like conveyor belt 14, moves at about 6 to 12' per minute.

The fiber which is laid down on conveyor belt 90 is subjected to three hot water washings, at stations 92, 94 and 96, and to a cold water washing, at station 98. These initial Washes remove substantially all of the impurities Which by the caustic treatment have become dislodgeable. At each of these stations, the Water is pumped from its'own tank 92A, 94A, 96A and 98A to a point just ahead of a pair of rolls 92B and C, 94B and C, 96B and C, and 98B and C through which the fiber is to pass.

As the fiber mass passes between rolls 92B and C, it is compressed by the rolls. During this compression, the liquid, which was applied to the mass at station 92, is dispersed in and among the fibers thereof, the excess liquid being expressed and collected in pan 92D. Similarly, rolls 94B and C and 96B and C compress the fiber as it passes between them, and the liquid, which is applied at stations 94 and 96 respectively, is dispersed in and among the fibers, the excess liquid being expressed and collected in pans 94D and 96D respectively.

The rate of advance of belt 90 is regulated to prevent undesirable build-up of fibers thereon. The actual speed Though not absolutely necessary,

of belt will, of course, depend on the desired pounds per hour throughput of the apparatus.

The distance between the point of application of the liquids at stations 92, 94, 96 and 98, and rolls 92B and C, 94B and C, 96B and C, and 98B and C respectively, should be sufficient to enable the liquids to penetrate the fiber mass. We have found that this distance should preferably be approximately 8-16 inches more or less at belt speeds of approximately 6 to l2 per minute.

While it is possible to have a separate fresh water supply for each station, we prefer to use a counter-current system and thereby take full advantage of the effects of chemicals dissolved into the wash Water at stations through which the fiber is about to pass. Accordingly, the wash water used at station 92, which was drained from pan 94D via line 92G, contains the greatest amount of contaminants. However, the web at station 92 contains so much more contaminants than are present in the wash solution that the wash at station 92 is highly effective. The wash solution collected in pan 92D is drained from pan 92D and removed from the system through line 92X.

'I'he wash Water from station 96 is drained from pan 96D via line 94G and delivered into tank 94A and thence is sprayed on the fiber mass as it progresses through station 94, and the water from tank 96A is sprayed on the liber mass that passes through station 96. Pumps 92E, 94E, 96E and 98E respectively, in lines 92F, 9413, 96F and 98F, furnish the needed power for spraying the wash solution. Sufiicient heat is furnished to tanks 92A, 94A and 96A to raise the temperature of the wash solution to about 160 F. more or less, since hot water is more efcient than cold water in washing the fiber free of caustic and other impurities which have become dislodgeable by the caustic treatment. Depending on what bleach solution is to be used immediately after station 98, heat may or may not be furnished to tank 98A. If peroxide is used, heat may be desirable. However, when a chlorinecontaining bleach is to be used, the bleaching process is ordinarily carried out at or near room temperature, and, therefore, no heat need be furnished. It is desirable to control the temperature of the liquid in tank 98A, so that the temperature of the liquid which is applied at station 98 is not materially different from the temperature of the bleach applied at station 100.

In each of these washes, as well as in all other washes which are hereinafter to be mentioned, the weight of the Wash solution preferably is approximately ten times the weight of the dry web. In accordance with well-known dilution principles, great water savings, and therefore great eliiciency in the utilization of Water, result from the utilization of a plurality of washes, followed each time by squeezing, over a single Wash utilizing an amount of water equal to the cumulative amount of wash solution. For example, while the use of 30 volumes of wash solution as a wash is perhaps as much as three times more effective than a wash using ten volumes, three lO-volume portions of water, each of which is expressed before the next is applied, may be as much as 100 times more effective than a single wash using l() volumes of wash solution.

While the washing after caustic treatment removes substantially all of the impurities of the bulk mass, a small, yet objectionable, amount of impurities remain therein. These can be removed or their effect neutralized by bleaching. Accordingly, after the fiber mass passes through station 98, it is treated with a bleach solution at station 100. The fiber saturated with bleach solution then passes through the nip of squeeze rolls 19GB and C, where the solution is thoroughly dispersed in and among the fibers of the bulk. The excess solution is expressed therefrom and collected in pan 100D, whence it is drained via line 100G into bleach makeup tank 100A. Pump 100E in line 100F furnishes the necessary power to spray the bleach solution on the web at station 100.

A wide variety of bleaching reagents may be satisfactorily employed in the process of our invention. Among these we include, but do not limit ourselves to, chlorine gas dissolved in water, hypochlorous acid, sodium hypochlorite, sodium perborate, calcium hypochlorte, lithium hypochlorte, sodium chlorite, the peroxides of hydrogen and sodium, as well as many others including certain mixtures of the above-mentioned bleaching reagents. The concentrations of the solutions will, of course, vary in accordance with the bleaching reagent used. While for the purpose of this invention we shall describe our process using our preferred bleaching reagent, sodium hypochlorite, it should be understood that we do not intend to limit our invention to the use of any particular bleaching reagent.

In accordance with this embodiment, a solution of sodium hypochlorte in water, having an available chlorine content of from 0.1% to 0.5% and preferably 0.3%, and preferably having a pH of from 9.5 to 11, is made up in tank 100A. This solution is delivered by pipe 100F to station 100 where it is sprayed on the ber. Approximately to 20 parts by weight of solution per part of ber (dry weight) are applied through the sprays, which are preferably positioned some 8 to 16 inches ahead of rolls 100B and 100C. As the web passes through rolls 100B and 100C, the liquid is evenly distributed in the ber mass, by the pressure applied to the rolls and the excess liquid is expressed and recovered in pan 100D. The pressure, which is applied to the rolls by some suitable means (not shown), is regulated so that a controlled amount of bleaching reagent is retained in the ber mass as it passes through the roll. Any suitable means for applying pressure to the rolls may be used.

Since the reaction between the bleaching reagent and the cotton impurities is not instantaneous, that is, requires some time to proceed to the desired point, we provide an age period during which the bleach and the brous mass remain in commingled relationship. This is done in much the same way that we provide for the caustic age as previously described. The saturated ber mass, which is in the form of a web as it leaves rolls 100B and 100C due to compression of the rolls, passes from belt 90 through pinned rolls 102 and 104 into another aging tower 106, where it remains for an age period of from minutes to three hours more or less. Of course, when bleaching reagents other than sodium hypochlorte are used, the age period may vary considerably beyond those time limits.

We nd that some varieties of bulk ber are more resistant to bleaching reagents than are others. We nd that with these varieties it is sometimes advantageous to continue to apply additional bleach solution to the ber for a period up to ve minutes, more or less, after the initial wetting and before the ber is admitted to the age tower. The retention of the ber in a wet condition while applying additional bleach solution to it affords a greater opportunity for the liquid to diffuse into the shell and other contaminants of the ber mass.

We refer to the short period during which the ber is held in the wet condition, while additional bleach is being applied thereto, as the wet hold-up time, and the step of continuing to provide solution to the wetted ber over a period of time as the wet hold-up step. While this step is being described with reference to the application of bleach solution, it should be appreciated that the step could be used advantageously inthe application of caustic or other treating chemical.

In carrying out this step, we apply the solution to the web, express the excess, and thereafter apply additional solution to the web for a period of up to 5 minutes more or less. Thereafter, We reduce the liquid remaining in the web to between about 75-400% of the weight of the web (dry basis), depending on the variety of ber which is being processed, and then deliver the ber to the age tower. We nd that we can accomplish the desired wet hold-up step by providing a secondary conveyor 112,

i0 which is located immediately after rolls 100B and 100C and before the age tower 106.

Secondary conveyor 112 is positioned at a slight distance above belt and moves independently thereof but in the same direction as belt 90. Conveyor belt 112 moves at a much slower speed than belt 90, and as the brous web is presented to belt 112, the web forms itself into pleats due to the difference in the speed of belts 90 and 112. Belt 112 is of suicient length and moves at sufciently slow speed to provide the desired retention time to the brous web which it carries.

In passing from belt 90 to belt 112, the web passes over roll 113, which is positioned just ahead of belt 112, and is of sufficient diameter to bridge the gap between belts 90 and 112. Roll 113 does not come in contact either with belt 90 or with belt 112, but moves in the same direction as both of these belts and at peripheral speed, which is approximately equal to the linear speed of belt 90. Accordingly, roll 113 lifts the web from belt 90 and deposits it on belt 112 where it is pleated. In place of roll 113, a nip roll assembly may be used to advantage to assure positive forward motion of the brous we Positioned above belt 112 are auxiliary sprays 112A, 112A and 112A, which furnish bleach solution to the pleated web which is carried by belt 112. The solution used in these sprays may be supplied from tank A through line 100F, as is indicated in the drawing, or may be supplied from a separate tank (not shown), which may contain the same bleach as tank 100A, or may contain a different bleach. A pan 112D is provided beneath belt 112 to collect the excess bleach solution which is applied to the web through sprays 112A, 112A and 112A" and line 112G which connects to pan 112D and returns the excess bleach to the bleach solution tank. When we use our wet hold-up step in conjunction with spray 100, we may use as much as 100 parts or more of solution per part of ber (dry basis). However, the excess solution (Le. excess over the 75-400% which we allow to remain associated with the ber in the age tower 106) is expressed by rolls 112B and 112C before the web passes into the age tower 106. The web passes over the end of belt 112 and returns to belt 90, where it is unpleated, and then is delivered to pinned rolls 102 and 104 which comminute and deliver it to the age tower 106.

After the age period the ber leaves the tower 106 by a conveyor belt 108 and passes into wet stock feeder 110, which fo1rns and delivers the ber preferably as a web to conveyor belt 114. The web is washed twice at stations 116 and 118, being squeezed after each washing by passing between rolls 116B and 116C and 118B and 118C, at which points the excess wash solutions are expressed, the excess being recovered in pans 116D and 118D.

The Wash solution from 116D s drained to tank 98A and the excess solution from station 118 is collected in rlSD, whence it is drained to tank 116A through line Having been twice washed after leaving rolls 118B and 118C, the web still retains traces of the bleach constituents which may not be desirable. In the case where sodium hypochlorte is used as the bleaching ingredient, such constituents are alkaline in nature. Since we prefer a substantially neutral or even slightly acidic web before applying the nal nish, we treat the web issuing from rolls 118B and 118C with a dilute solution of an acid, preferably an inexpensive organic or inorganic acid such as sulphuric, acetic, hydrochloric or phosphoric, and fol- 10W this acid treatment with two washes before nally applying a suitable final nish treatment.

The acid is preferably a dilute solution having a concentration of 1% or less and about 10 to 15 parts of acid solution per part of ber are applied at stations 120 and 122. The acid is made up in tank 120A and is pumped by pump 120E through line 120F to stations 120 and 122, where it is sprayed on the web. The web passes through 11 rolls 120B `and 120C and 122B and 122C, where the excess acid is expressed or distributed as above described. The acid is collected in pans 120D and 122D and returned to tank 120A via line 120G and line 122G.

The web is again washed prior to applying the finishing solution. This is done at stations 124 and 126. The final washing is accomplished at station 126 where the fresh water, which is supplied to the process, is introduced. This water from main 128 is first brought to a suitable temperature in heat exchanger 130 and conveyed via line 132 to station 126. The temperature of this water is not critical, but in order to maintain controlled washing conditions, we prefer to use a constant temperature of about '85 F. Except as otherwise indicated, we prefer to carry out all other steps of our process at this temperature. The web passes through rolls 126B and 126C, the excess Water being expressed therefrom and collected in pan 126D, whence it passes via line 124G to tank 124A. From tank 124A the wash water is pumped via line 124F through pump 124B to station 124. The excess Water is expressed from the web by the rolls 124B and 124C, passes into pan 124D, whence it passes into tank 118A via line 118G.

Thus it will be appreciated that while en route through our process the web may be washed as many as or more times, yet it is only necessary for us to introduce sufficient water for a single washing and introduce this fresh water at a single station. Thus by taking advantage of a counter-current system, we realize tremendous savings of water as well as time and manpower. Furthermore, the clean wash water, which is admitted to our process, first cornes in contact with the web after it is substantially free of all foreign matter. In subsequent washings the water is further contaminated, but at all points where the wash water is reused on the web the concentration of impurities on the web is much greater than the concentration of impurities in the water. Accordingly, the washings are thoroughly effective.

Of course, it will be appreciated that our process may be carried out without utilizing the counter-current wash water system, and we do not intend to limit or restrict our invention to the use of counter-current wash water systems. However, the utilization of the counter-current wash water principle is of extreme importance since, in substantially every instance where wash water is reused, the ingredients which it contains as a result of its previous history conditions the web for more effective reaction with the treating chemicals which follow the washing as the web progresses through the process.

As a nal treatment, we apply a nishing solution at stations 134 and 136. The finishing solution may be made of any well-known finishing materials and their selection depends on the particular properties which are desired for the end product. There are, of course, many soaps and other finishing mixtures which are commercially available and are suitable in accordance with our invention. One such recipe is as follows:

400 grams of stearate soap 100 gallons of water Acetic acid to adjust the pH of the solution to 4.5

The solution is made up in tank 134A and passes via line 134F and pump 134B to stations 134 and 136, where it is sprayed on the web. The excess solution is expressed from the web as it passes through rolls 134B and 134C `and 136B and 136C. The web leaving rolls 136B and 136C is conveyed on belt 114 to suitable drying and `storing facilities (not sho'wn).

The process herein above described may be modified in many ways, particularly in the use of bleaching reagents and in the washing procedures which follow the application of the bleach. For example, we have successfully used an acid hypochlorite instead of sodium hypochlorite in tank 100A. Following this procedure we nd it unnecessary to treat the web with sulphuric acid in stations 120 and 122. Alternatively, we can use acid hypochlorite from tank 100A and interpose an additional station (not shown) after station 118, for reacting the web with the sodium hypochlorite solution and follow this treatment with the sulphuric acid wash.

Some of these modifications will best be understood by referring to the following examples:

Example: l-Bales of cotton fiber waste material known as comber waste were fed by an appropriate means into bale opener 10 and thence into ber feeder 12. This fiber feeder was set to operate at a rate of 400 pounds (dry weight) per hour. The cotton was delivered onto conveyor 14 as a continuous web, and a solution of caustic soda, soap, pine oil, wetting agent, and chelating agent were applied to the moving web. The solution contained 4% sodium hydroxide, 0.8% low titre soap (consisting primarily of sodium oleate, but also sodium stearato in lesser proportion), 0.4% pine oil, 0.2% of a non-ionic wetting agent and 0.05% of a chelating agent. Solution was applied to the cotton by pumping it to a plurality of ooders and sprays 20 and the wetted web was passed through nips 24 of roller 26. The temperature of the solution was 200F. Approximately 20 parts of solution per part of fiber were applied. The web was again saturated at a plurality of ooders and sprays 20A and again squeezed by nip 24A of roller 26A, the amount of solution on the fiber being reduced to a weight ratio of approximately 1.25 to 1.0. The wetted fiber was then aged in substantial absence of air by contacting it directly with steam for 60 minutes at a temperature of 212 F. in age tower 36. The fiber leaving tage tower 36 was formed as a web on wire screen conveyor and was washed with a succession of four sprays interspersed with four squeezings. The first three sprays were applied at stations 92, 94 and 96. The sprays consisted of hot Water recirculated counter-current. Cold water also recirculated counter-current was applied at station 93. Each application of liquid was at a ratio of l0 parts per part of fiber. The squeezing action reduced the amount of liquid on the fiber to a ratio of 1.0 to 1.0. The web was then spray-saturated at station with a sodium hypoehlorite solution containing 0.3% available chlorine at a pH of 10.2 and a temperature of 95F. Approximately ten parts of solution were applied per part of fiber. The web was then passed through squeeze rolls and the amount of liquid on the ber reduced to a ratio of 1.0 to 1.0. Additional hypochlorite solution was applied to the moving web in a ratio of approximately 50 parts of liquid per part of fiber at station 112. The

web was retained in a saturated condition for 3.5 minutes by pleating it onto conveyor 112 while being continuously saturated with solution at sprays 112A, 112A and 112A. After leaving belt 112 in a soaking wet condition, the web was unpleated onto conveyor 90 and the amount of liquid on the web reduced to a ratio of 3.0 to 1.0 by passing through squeeze rolls. The fiber was then deposited in bleach age tower 106 for an aging period of 60 minutes. Upon removal from the tower, the fiber was reformed as a web on conveyor 114. Here it was treated in web form by a series of sprays and squeezes alternately applied. The web was rst washed with water (approximately 10 parts per part of fiber) at 85F. supplied counter-current at stations 116 and 118. At each station the amount of liquid remaining on the fiber was reduced to a ratio of approximately 1.0 to 1.0 by squeezing. After washing, the web was passed through stations and 122, where an acid-souring solution was applied. The solution used consisted of 0.5% sulphuric acid at a temperature of 85F. At each station, the amount of liquid applied was approximately at a ratio of 10 parts per part of fiber and the squeezing reduced the amount of liquid on the fiber to an approximate ratio of 1.0 to 1.0. Subsequent to the acid treatment, the web was again washed with water at 85 F. supplied counter-current at stations 124 and 126. Approximately parts of liquid per part of fiber were applied to each station, and the rolls reduced the amount of liquid memaining on the fiber to an approximate ratio of 1.0 to 1.0. The fresh water for the countercurrent washings herein above referred to was introduced at station 126. The fiber was then treated with finishing solution at stations 134 and 136. The finishing solution consisted of an 0.1% by weight solution of sodium stearate in water at 125 F. reduced in pH to 4.5 with acetic acid. The finish solution was applied at each station in a ratio of 10 parts of liquid per part of lfiber and the squeezing action reduced the amount of liquid on the fiber to an approximate ratio of 1.0 to 1.0. The fiber (approximately 400 lbs. per hour) was removed from belt 114 and was dried. It was found to be highly absorbent, exceptionally white and free of impurities. This cotton met all U.S.P. specifications. The cellulose viscosity of this cotton as measured by the well-known cupriethylenediamine technique was found to be satisfactory and the fiber was found to be completely acceptable for general use -as `a bleached, purified absorbent bulk cotton.

Example 2.-Bulk cotton of the type set forth in Ex, ample 1 is treated by the method set forth in Example 1 upto the point of application of bleach solution. Following the wash at station 98, an acid bleach solution containing approximately 0.25% available chlorine at a pH of 4.0 to 5.0 and a temperature of 60 F. is applied to the web at stations 100 and 112. The amount of solution on the fiber is adjusted to an approximate ratio of 1.0 to 1.0 by passing the web through rolls 112B and 112C. The fiber is then aged for 30 minutes in age tower 106. Following aging, the fiber is washed. After washing, finish is applied as in Example l.

Example 3.-Two hundred pounds per hour of bulk cotton ber of the type set forth in Example 1 was processed by the techniques set forth in Example 1 up to the point where bleach solution is applied at station 100. At this point acid bleach (hypochlorous acid) containing 0.25% available chlorine at a pH of 4.5 and a temperature of 60 F. was applied to the web by a series of two sprays followed each time by a squeeze. At each point where the bleach was applied, solution in the amount of approximately 10 parts of solution per part of fiber was used. The liquid content in the web was reduced by squeeze rolls to an approximate ratio of 1.0 to 1.0. Following this bleach solution treatment, the web was aged in tower 106 for a period of 30 minutes. Following this, the fibers were reformed as a web, which was washed with water at 85 F. and then subjected to treatment with sodium hypochlorite solution containing 0.15% available chlorine at a pH of 11.0 and a temperature of 85 F. The solution was applied in two stations and following each application the web was squeezed by passing through rollers so as to adjust the amount of liquid on the fiber to a ratio of approximately 1.0 to 1.0. Following this, the web was washed, treated with acid, rewashed and treated with a finishing solution as previously described in Example 1.

Example 4.-Bulk cotton of the type set forth in Example 1 is treated by the method as therein described up to the point where bleach solution is applied at station 100. At this point, an alkaline solution of hydrogen peroxide containing hydrogen peroxide in amount corresponding to 0.3% by weight at a pH of from 10 to 12 and a temperature of 200 F. and containing 1.5% sodium silicate buffer-stabilizer is applied to the web by a series of two sprays followed each time by a squeeze. At `each point where the bleach is applied, solution in the amount of approximately 10 parts per part of fiber is used. The liquid content in the web is reduced by squeeze rolls to an approximate ratio of 1.0 to 1.0. Following this bleach solution treatment, the web is aged in tower 106 for a period of 60 minutes in direct contact with an air-stream mixture at a temperature of 170 F. Upon removal from tower 106, the fiber is reformed as a web on conveyor 114 and is washed, soured, washed and treated with finishing solution by the method set forth in Example l.

This application is a continuation of application Serial No. 603,127, filed on August 9, 1956, and now abandoned.

Having thus described our invention, we claim:

1. The method of continuously purifying bulk unbleached cotton fibers including the steps of forming an uncompacted layer of said fibers, supporting said layer on a continuously moving conveyor belt, saturating said layer with a 1-8% aqueous solution of sodium hydroxide between about 150 F. and 212 F., compressing said layer while on said conveyor belt to distribute said solution uniformly throughout said layer, again saturating said layer with said aqueous solution, compressing said layer to reduce the amount of solution on the fiber to a weight ratio of about 1.25 to 1.0, removing said fibers from said conveyor belt and allowing said solution to react with said layer for about 60 minutes at 212 F. in the presence of steam and in the absence of air, thereafter again forming said fibers into an uncompacted layer and supporting them on a second continuously moving conveyor belt, washing said fibers and saturating said fibers with a solution of hypochlorous acid at about 60 F. having a pH of about 4.5 and about 0.25% available chlorine, expressing the major portion of said hypochlorous acid solution to distribute said solution uniformly among said fibers and to reduce the liquid content of the mass to an approximate ratio of about 1.0 to 1.0, allowing said solution to react with said fibers for a period of about 30 minutes, washing said fibers, and thereafter subjecting said fibers to treatment with a solution of sodium hypochlorite at about F., having a pH of about 11.0 and about 0.15 available chlorine with the liquid content of the mass in a ratio of about 1.0 to 1.0, said steps occurring sequentially and continuously with only a portion of the total bulk of said fibers being subjected to any one of said steps at a given time.

2. The method of continuously purifying bulk unbleached cotton fibers including the steps of forming an uncompacted layer of said fibers, supporting said layer on a continuously moving conveyor belt, saturating said layer with a 1-8% solution of sodium hydroxide between about F. and 212 F., compressing said layer while on said conveyor belt to distribute said solution uniformly throughout said layer, again saturating said layer with said solution, compressing said layer to reduce the amount of solution on the fiber to a weight ratio of about 1.25 to 1.0, removing said fibers from said conveyor belt and allowing said solution to react with said layer for about 60 minutes at 212 F. in the presence of steam and in the absence of air, and thereafter washing and bleaching said fibers, said steps occurring sequentially and continuously with only `a portion of the total bulk of said fibers being subjected to any one of said steps at a given time.

3. The method of continuously treating bulk unbleached cotton fibers which have previously been subjected to steam and caustic treatment, said method including the steps of washing said fibers with water, saturating said fibers with a solution of hypochlorous acid at about 60 F. having a pH of about 4.5 and about 0.25% available chlorine, expressing the major portion of said solution to distribute said solution uniformly among said fibers and to reduce the liquid content of the mass to an approximate ratio of about 1.0 to 1.0, allowing said solution to react with said fibers for a period of about 30 minutes, washing said fibers, and thereafter subjecting said fibers to treatment with a solution of sodium hypochlorite at about 85 F., having a pH of about 11.0 and about 0.15 available ch-lorine with the liquid content of the mass in a ratio 0f about 1.0 to 1.0, said steps occurring sequentially and continuously with only a portion of the total bulk of said fibers being subjected to any one of said steps at a given time.

4. A process for continuously bleaching bulk cotton textile fibers which have previously been subjected to steam and caustic treatment, said process including the steps of Washing said fibers with water, saturating a web of said fibers with about 10 parts of a solution of hypochlorous acid per part of fibers, said solution being at about 60 F. and having a pH of between 4.0 and 5.0 and about 0.25% available chlorine, expressing said solutions from said web to reduce the liquid content in the web to a ratio of 1.0 to 1.0, promptly thereafter again similarly saturating said web with a similar portion of said hypochlorous acid solution and similarly reducing said liquid content, and thereafter allowing said solution to react with said hypochlorous acid solution for approximately 30 minutes.

5. The process of claim 4 followed by the step of neutralizing said acid solution and bleaching said fibers by contacting said web with a solution of an alkaline oxidizing reagent.

6. The process for continuously bleaching bulk cotton fibers which have previously been wetted and subjected to caustic treatment, said process including the steps of washing said fibers with water, continuously saturating a web of said fibers with a solution of sodium hypochlorite at a temperature of 95 F., said solution having from 1.5 to 10 grams of available chlorine per liter Vand a pH of from 9.() to 12.0, compacting said web in a pleated configuration and continuously saturating it with additional portions of said hypochlorite solution for a period no greater than about 5 minutes, and thereafter reducing the -amount of liquid in the web to a ratio of about 3.0 to 1.0 and allowing said solution to react with said bers for about 60 minutes, zsaid steps occurring sequentially and continuously with only a portion of the total bulk of said iibers being subjected to `any one of said steps at a given time.

7. The process for continuously treating bulk unbleached cotton bers including the steps of forming an uncompacted layer of said fibers, supporting said layer on a moving conveyor belt, spraying said layer with an aqueous solution of bleaching solution taken from the group consisting of hypochlorous acid and sodium hypochlorite to impregnate said layer with said solution, compressing said laye'r while on said conveyor belt to distribute said aqueous solution uniformly throughout said layer and to reduce the amount of liquid in said layer to a ratio of between about 3.0 to 1.0 and 1.0 to 1.0, said 16 solution having from 1.0 to 10 grams of available chlorine per liter and being at a temperature between F. and F., and thereafter allowing said solution to react with said layer for between about 30 and about 60 minutes.

8. The process for continuously treating bulk unbleached cotton fibers including the steps of forming an uncompacted layer of said fibers, supporting said layer on a moving conveyor belt, spraying said layer with an aqueous solution of bleaching solution taken from the group consisting of hypochlorous acid and sodium hypochlorite to impregnate said layer with said solution, compacting said layer and continuously saturating it with a similar portion of said aqueous bleaching agent for a period no greater than about 5 minutes, compressing said layer while on said conveyor belt to distribute said solution uniformly throughout said layer and to reduce the amount of liquid in said layer to a ratio of between about 3.0 to 1.0 and 1.0 to 1.0, said solution having from 1.0 to 10 grams of available chlorine per liter and being at a temperature between 60 F. and 95 F., and thereafter allowing said solution to react with said layer for between about 30 and about 60 minutes.

9. The process for continuously treating bulk unbleached cotton fibers including the continuous steps of forming an uncompacted layer of said iibers, supporting said layer on a moving conveyor belt, spraying said layer with an aqueous solution of bleaching solution taken from the group consisting of hypochlorous acid and sodium hypochlorite to impregnate said layer with said solution, compressing said layer while on said conveyor belt to distribute said solution uniformly throughout said layer, promptly thereafter saturating said layer with a similar portion of said aqueous bleaching agent for a period of between about 3.5 and 5 minutes, compressing said layer to distribute said solution uniformly throughout said layer and to reduce the amount of liquid in said layer to a ratio of between about 3.0 to 1.0 and 1.0 to 1.0, said solution having from 1.0 to l0 grams of available chlorine per liter and beingr at a temperature between 60 F. and 95 F., and thereafter allowing said solution to react with said layer for between about 30 and about 60 minutes.

References Cited in the file of this patent UNITED STATES PATENTS 2,253,242 MacMahon et al Aug. 19, 1941 2,602,723 Rogers July 8, 1952 2,686,102 Hawkes et al Aug. 10, 1954 

1. THE METHOD OF CONTINUOUSLY PURIFYING BULK UNBLEACHED COTTON FIBERS INCLUDING THE STEPS OF FORMING AN UNCOMPACTED LAYER OF SAID FIBERS, SUPPORTING SAID LAYER ON A CONTINUOUSLY MOVING CONVEYOR BELT, SATURATING SAID LAYER WITH A 1-8% AQUEOUS SOLUTION OF SODIUM HYDROXIDE BETWEEN ABOUT 150*F. AND 212*F., COMPRESSING SAID LAYER WHILE ON SAID CONVEYOR BELT TO DISTRIBUTE SAID SOLUTION UNIFORMLY THROUGHOUT SAID LAYER, AGAIN SATURATING SAID LAYER WITH SAID AQUEOUS SOLUTION, COMPRESSING SAID LAYER TO REDUCE THE AMOUNT OF SOLUTION ON THE FIBER TO A WEIGHT RATIO OF ABOUT 1.25 TO 1.0, REMOVING SAID FIBERS FROM SAID CONVEYOR BELT AND ALLOWING SAID SOLUTION TO REACT WITH SAID LAYER FOR ABOUT 60 MINUTES AT 212*F. IN THE PRESENCE OF STREAM AND IN THE ABSENCE OF AIR, THEREAFTER AGAIN FORMING SAID FIBERS INTO AN UNCOMPACTED LAYER AND SUPPORTING THEM ON A SECOND CONTINUOUSLY MOVING CON- 